VORTEX-SE and the 3 March 2019 Tornado Outbreak

The “Meso18-19” field project of VORTEX-SE held its sixth Intensive Observing Period (IOP) of the tornado season on 2-3 March 2019. Sadly, a long-track EF4 tornado in this event killed at least 23 people in Lee County, Alabama. As I write this, several NWS offices are conducting damage surveys in Alabama, Georgia, and Florida, and it may be a while before we know the final tornado count. As I watched this event unfold, I saw numerous radar signatures of what appeared to be fairly significant tornadoes, with strong velocity couplets and debris signatures.

We first noticed this event taking shape early in the week, as the European forecast model showed a pattern of strong low-level winds and substantial CAPE centered roughly in the Tennessee River Valley region. At that time, the U.S. forecast models were not showing any suggestion of this pattern. So we went into “IOP WATCH” mode to see if the models would come into more of a consensus regarding the threat. With time, the US models did start moving toward a more threatening forecast, so we had (barely) enough confidence to declare IOP #6. Recall that our general plan is to observe the atmosphere for a full 48 hours, ending when the severe weather ends or departs our domain (this roughly means moving east of an Atlanta-Tallahassee line). And we need 48 hours to line up the personnel, resources, and accommodations to make our observations. So we have to commit ourselves to the plan at roughly day4-5 of the SPCs Convective Outlook. This is, frankly, pretty stressful because of the huge uncertainy that is generally present in a 96-hour forecast of tornadoes!

As the event approached, we started turning our attention to the “Convection-Allowing Models” (CAMs) such as the HRRR, the NAM-3km, and other similar models. We looked at the “UH tracks” (this stands for Updraft Helicity, a measure of the rotation of the updrafts in the model). We started seeing ominous signs of tornado threat with tracks across mainly Alabama, and a few into Georgia. By Saturday, it became clear that the threat that first caught our eye in the European forecast model was real, but that it was going to be shifted much closer to the Gulf Coast.

We began our special soundings from our university and NOAA-lab operated sites, and 13 NWS regular sounding sites, at midday Saturday. At that time, there was no CAPE or shear supportive of tornadoes to be found in the Southeast. The upper system was just moving into the Southwest US. By 6 AM Sunday morning, the potentially unstable air was just beginning to come onshore from the Gulf of Mexico, first showing up in our Breaux Bridge, Louisiana soundings (conducted by the University of Louisiana-Monroe), and the Slidell LA NWS sounding. An additional sounding in mid-morning from our team at Mobile, AL (University of South Alabama) showed the rich airmass onshore in Mobile at that time. And by mid-morning Sunday, the big acceleration in the low-level winds across MS and AL had begun, so it was just a matter of time before the tornado-supporting flow and the rich Gulf air near the ground started overlapping in southeast MS, southern LA, and southern GA.

This season has featured a very large temperature contrast between the continental U.S., where many of us have been shivering, and the warm air masses to the south (such as over the Gulf of Mexico). This temperature contrast drives the strong westerly winds aloft and their embedded waves, and so we have repeatedly had strong low pressure systems capable of bringing warm humid air onshore and strong low-level wind shear supportive of tornadoes. Yesterday’s system brought together the strong shear with a bit higher CAPE than we have seen with the other systems, and the result was devastating. Unfortunately, there is no real end in sight to this energetic pattern.

During yesterday’s event, VORTEX-SE special soundings were being used by forecasters at the Storm Prediction Center and at the NWS forecast offices to help anticipate the degree of tornado threat. I was very impressed with how well forecasters were able to fine-tune the short-term outlooks and provide quality warnings. The sad loss of life tells me that we have to continue to work on making sure everyone understands, and is able to respond to, the information coming out of the NWS and communicated so effectively by the media and others.

VORTEX-SE stands to learn a lot from these events. We will get a clearer picture of whether/not/how additional observations can improve the numerical forecast models. With time, it’s almost certain that the forecast models can show tornado threat and even estimate likely tornado intensity with lead times of hours. That is the goal, anyway. The VORTEX-SE work is important in advancing this capability. In parallel, VORTEX-SE is supporting a lot of research (some of it happening today in Alabama) into how people respond to tornado forecasts and what obstacles stand in the way of getting people into shelter locations that can withstand the expected tornado winds. As forecasts continue to improve, we ought to be able to help people make reasonable sheltering decisions even if their homes are too fragile to withstand typical tornado winds.

I think I speak for most of the VORTEX-SE researchers in saying that tragedies like yesterday’s Lee County tornadoes hit us pretty hard. There’s no relishing or enjoyment. But that said, these events are the reason most of us do what we do, and motivate us to keep moving forward in this research.

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STATUS: 22 Feb 2019

Our fifth Intensive Observing Period of this cool season began at 6 AM this morning with special sounding launches from ten sites operated by universities and NOAA labs. The information from these soundings is going to be valuable as an intense low pressure system develops in the Plains later today. In collaboration with the NWS, VORTEX-SE will perform special soundings every six hours through 6 AM Sunday morning. By Sunday morning, the cold front with this particular weather system will have swept most of the way out of our observing domain. These are the sounding sites that are being used:

As this weather system sweeps across the Southeast, it looks like the storms will have the potential to produce tornadoes. Right now, the models show the greatest threat extending across northern LA and southeast AR, through the northern half of MS, and into western TN and northern AL. The severe weather should develop around midday Saturday, and move quickly northeast to AL and middle TN by late Saturday evening. There may be a few relatively isolated supercells ahead of the main band of activity, and then the main band of activity will probably be comprised of fairly tightly spaced supercells. At 11:30 AM CST the SPC issued this outlook:

Some of the uncertainties with this system include the expected tornado intensity, the northern and southern extents of the threat, and how late into the evening on Saturday (and how far north and east) the activity will persist. Often with these systems that appear to have a pretty high threat, there is some unexpected or poorly understood aspect that ends up limiting the threat. These limits to the threat are as important to understand as the factors that come together to produce the threat.
An additional complication with this system is the tremendous amount of rain and consequent flooding that has occurred, and will continue, across northern AL, TN, northern MS, and adjacent regions. These “multiple-hazard” events are not unusual in the Southeast, and complicate the work of all involved in the weather enterprise.

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STATUS: 19 February 2019 IOP #4

The VORTEX-SE field program, “Meso18-19” is conducting its fourth Intensive Observing Period across the Southeast. This began at 6 AM today and will continue into Wednesday night. Soundings are being launched from 13 NWS sites, and 10 sites operated by universities and NOAA labs, every six hours. Additional more detailed observations will kick in across northern AL if the system moves that far north.

There is a warm front just offshore in the Gulf of Mexico. The suite of forecast models have varying solutions regarding how far inland this warm front will move tonight and tomorrow. The air to the south of the front has enough CAPE to support storms with low-level updrafts suitable for some tornado potential. To the north, the air is very cool and, based on our present understanding, tornadoes are nearly impossible.

The low-level shear to the north of the warm front is immense because of the temperature contrast between the two airmasses. Of more concern, though, will be the shape and length of the low-level hodograph in the warmer, humid air once the front moves inland.

These sorts of situations, with great uncertainty about the return of warm humid air off of the Gulf of Mexico, are not uncommon in the Southeast. In our previous years’ field campaigns, this uncertainty made it difficult for the scientists to anticipate the likelihood of storms, and their tornado potential.

VORTEX-SE includes research into how we can most effectively communicate about multiple ongoing hazards… a common situation in the Southeast. This event is no exception, with heavy rainfall and possible associated flash flooding a real threat across portions of the region. This event also illustrates one of the difficulties of threat perception: it is February, and temperatures across the region are predominantly in the 40s with cold rain. This doesn’t feel like tornado weather, and if the tornado threat does develop tonight or tomorrow, it may only “feel like” tornadoes for a short time before they occur.

We may wrap up our observations for this case a bit earlier than we normally would in order to give all of the participants time to rest and plan for another IOP on Friday and Saturday. Current models are showing a potent setup, with tornado potential across AR, northern MS, TN, and northern AL. Of course, this forecast will change (this blog is NOT an official forecast!). But in Meso18-19, we must decide on IOPs at least 48 hours in advance to give all the participants adequate time to prepare, and so for a Friday morning start… today was decision day. Stay tuned.

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STATUS: 28 November 2018 IOP #2

With the news being about Midwest blizzards, Black Friday, and Cyber Monday, it doesn’t seem right that VORTEX-SE should be active. But we are.

Over the last couple of years, we have grown increasingly concerned about observing the “cool season” tornado events in the Southeast.

The peak occurrence of killer tornadoes in the Southeast spans a broad season from October through early May. Tornadoes this time of year are especially concerning because of the perception that tornadoes are a springtime phenomenon. People let their guard down during the fall and winter.

On Friday, an upper wave and jet stream will be plowing into the Southern Plains. As pressures fall, strong low-level flow will develop off of the Gulf of Mexico, transporting warm humid air inland. Combined with the upper level jet stream flow, profiles of temperature, humidity, and wind ought to become favorable for increased tornado potential, first in east TX, LA, and AR Friday evening, and spreading east into MS Friday night (30 Nov). The system will then chug east into AL/GA on Saturday. At some point, it will outrun the richer Gulf moisture and move into the cooler drier continental air left behind by the last system over the eastern US, and the tornado threat should diminish.

This cool season, VORTEX-SE will be doing an experiment aimed primarily at improving forecasts of tornadoes on time scales from a few hours to about 2 days. Starting at about the time the upper system enters the Plains, many Southeast NWS sites will be launching soundings every six hours, continuing for 48 hours. In addition, university and NOAA Lab partners will be launching soundings at the same times from College Station TX (Texas A&M), Fort Smith AR (NSSL), Monroe and Breaux Bridge LA (University of Louisiana at Monroe), Memphis TN and Starkville MS (Mississippi State), Mobile AL (University of South Alabama), Huntsville AL (University of Alabama-Huntsville), and Montgomery AL and Oak Ridge TN (NOAA Air Resources Lab, Atmospheric Turbulence and Diffusion Division).

In addition to this regional-scale observing campaign, we will be doing “nested” finer-scale observations in northern AL to get a look the details of the features we detect moving through the larger domain. This will include two “CLAMPS” profiling systems from NSSL and OU, as well as profiling, mobile radar, and mobile sounding systems from the University of Alabama-Huntsville. And the Texas Tech instrumented surface network (“Stesonet”) will be making observations across northern AL and southern TN, with instruments spaced roughly in every county.

All of this is part of the ongoing VORTEX-SE effort to improve the forecasting of, and human response to, tornadoes in the Southeast. These tornadoes are unlike their Plains counterparts in that they occur across a longer part of the year, are much more likely to occur at night, and occur in complex scenarios and from storm types that just have not been studied very well in the past.


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STATUS UPDATE: 3:53 PM CT 13 April 2018


The NOAA P-3 aircraft is operating in the Shreveport area. In the next 45 minutes, the SMART-Radars will be set up and operating in the area north of Shreveport.

About 1.5 hours ago, several cells exhibited decent rotation in NE TX. These persisted for about 45 min, and then weakened. The mobile sounding launched by U. Louisiana-Monroe, just east of Shreveport, looks like it would support severe storms, but instead we are in a downhill trend and a lull. The atmosphere is always interesting!

If I get a chance and activity picks up, I will post another update.

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STATUS: 13 April 2018


We will be using a special ad hoc subdomain today to maximize our radar data collection on the kind of weather that is most interesting. This decision is based on the logistics of our deployment… this is the last mission day for the NOAA P-3 aircraft, and if we wait for the interesting weather to get to the Monroe subdomain, the P-3 will no longer be able to work it. So we are deploying the two University of Oklahoma SMART-Radars to northwest Louisiana, to operate in conjunction with the Shreveport NWS WSR-88D. The NOAA P-3 aircraft will operate over this subdomain.

(Thunder in Norman as I write… a welcome sound!)

We expect supercells or clusters of supercells today in the subdomain, with the possibility of tornadoes occurring within our radar area.

The radars and aircraft are expected to be operating sometime around 3 PM.

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STATUS: 10 April 2018

STATUS: Down, but an IOP is likely on Friday 13 April.

The next major wave to impact the SE US will be moving into the area on Friday. We expect conditions possibly supportive of tornadic supercells or a QLCS Friday afternoon and night, but the location is not very certain. We will probably use the Monroe LA subdomain, but because this is the last possible mission day for the NOAA P-3 aircraft in VORTEX-SE this year, we may set up an ad hoc subdomain further we toward Shreveport if that’s where the weather takes us.

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STATUS: 6 April 2018


Mobile radar deployment is underway in the NE Louisiana subdomain, with scanning beginning about 2:30 PM. The NOAA P-3 research aircraft will be taking off around that same time, arriving in the subdomain area around 3:30 PM. Mobile and fixed soundings will be launched this afternoon.

Our expectations are very much in line with the SPC Day1 outlook. There may be isolated or scattered storms in the “warm sector” across Louisiana by mid-afternoon. These will be very hard to predict, but we will study any that happen in our subdomain. They may have rotation, but it’s not clear how persistent individual cells will be. The CAM forecast models don’t seem to be depicting long-lived supercells for reasons unknown.

A more linear, more predictable band of storms will organize in far southern AR by mid-afternoon, and sag southward through the evening hours. It should be near the AR/LA border around 3-5 PM, and near Monroe by 5-7 PM. Initially, this band may not be dominated by cold outflow, and so there is some potential for non-classic tornadoes during its first few hours. These tornadoes that are not associated with classic, isolated supercells are a special interest of VORTEX-SE. Toward evening, the band will likely accelerate south and be dominated by cold outflow, with diminishing tornado potential.

So we will probably have a good case to test new ideas about combining multiple radars of various types to obtain better characterization of the flow features in the storms that may promote or reduce tornado potential.

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STATUS: 5 April 2018

STATUS: IOP tomorrow 6 April

The U. Oklahoma SMART-Radars will be moving to the Monroe LA area shortly, and the P-3 will likely have an afternoon-evening flight tomorrow. We expect a near-certainty of strong convection in the U. Louisiana-Monroe subdomain, and this should prove useful for honing our ability to produce wind analyses based on a mix of multiple fixed, mobile, and airborne Doppler radars. At this time, it appears the main band of convection will pass through our subdomain between about 3-10 PM. We expect this main band to be elevated, with rotating updrafts but only slight possibilities of tornadoes. Of course… expectations can change, and reality has a way of telling us what we should have expected.

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